1. Field of the Invention
The present invention relates to a power circuit applicable to a hand held electronic device that employs a battery as a drive power. In detail, when a built-in battery and an external battery are used, and a voltage of the external battery is set to a predetermined voltage or more, a charge is driven by a voltage of the external battery. In addition, when the voltage of the external battery is lowered to the predetermined voltage or less, an arrangement is provided so as to drive a charge by means of the built-in battery. In this manner, an external battery can be replaced with the replacement battery without instantaneously interrupting an operation state of an electronic device.
2. Description of the Related Art
As an electronic device for battery driving, there is particularly known a hand held electronic device such as hand held telephone set, a notebook type personal computer (note PC), digital camera, digital video camera, or game device.
In such a hand held electronic device, there are many cases in which an external battery using a primary battery or a secondary battery or the like is used as a drive power supply, and a buffer amplifier battery (built-in battery) for preventing erasure of the contents of the built-in memory is incorporated.
In the meantime, in such an electronic device, when an external battery is used as a power supply, namely, during operation of the electronic device, there may occur a circumference in which a voltage of the external battery is lowered, and this battery must be replaced with the replacement battery.
In order to replace a battery, it is required to remove an external battery in use from an electronic device. At this time, a power supply to the electronic device is interrupted. If power supply is interrupted, even an electronic device in operation stops its operation. Therefore, even after battery replacement, when an attempt is made to continue the current operation mode, it is required to initiate the operation mode again.
In a notebook type personal computer or the like, if a power voltage is lowered to a certain voltage, its operation state is automatically written in a memory means such as a hard disk. Thus, information written after battery replacement is read out, thereby making it possible to restore the current mode to its original operation state.
However, in this case as well, for example, when communication is made using a public telephone line, for example, the public telephone line is cut off by removing the battery and turning OFF the power. Therefore, in this case, it is required to carry out line connection processing again.
The buffer amplifier built-in battery is available for use in a battery amplifier for the built-in memory, and does not function as a load drive battery when an external battery is removed.
In order to extend a time for using an external battery, although a battery having its large battery capacity may be used, such a battery is large in size, and is heavy in weight. Therefore, it is not advisable that such a battery with its large capacity is used as an external battery for a hand held electronic device.
The present invention has been made to solve such conventional problems. In particular, it proposes a power circuit, a power supply method, and an electronic device comprising the power circuit in which a build-in battery is used as charge driving during replacement of an external battery, thereby keeping continuity of an operation state even during replacement of the external battery.
In order to solve the above described problems, a power circuit according to the present invention comprises:
a first battery for driving a charge;
a second battery for driving the charge in place of the first battery;
a voltage detection means for detecting a terminal voltage of the first battery;
a first switch for controlling a power supply path of the second battery based on an output of the voltage detection means;
an overcharge prevention means for preventing an overcharge for the second battery caused by the first battery; and
a second switch connected to a charge path for the second battery and controlled by the output of the overcharge prevention means, the power circuit being characterized in that, when the first battery is lowered to a predetermined voltage or less, the charge is driven by means of the second battery.
In the present invention, an external battery (first battery) and a built-in battery (second battery) are provided. When external battery replacement caused by lowering of a terminal voltage, the built-in battery is used as a charge drive power supply.
By doing this, a charge continues its drive state by means of the built-in battery. Thus, even while an external battery is removed, a device can be used. Therefore, when communication is made by connecting a terminal device such as personal computer to a public telephone line, even if external battery replacement is required, such replacement work can be executed while communication is continued.
In order to solve the foregoing problems, a power supply method according to the present invention comprises:
a voltage detection step of detecting a terminal voltage of a first battery for driving a charge;
a step of controlling a first switch connected to a power supply path of a second battery for driving the charge in place of the first battery based on the result of the voltage detection step;
an overcharge prevention step of preventing an overcharge for the second battery caused by the first battery; and
a step of controlling a second switch for preventing an overcharge connected to a charge path for the second battery based on the result of the overcharge preventing step, said power supply method characterized in that, when the first battery is lowered to a predetermined voltage or less, the charge is driven by the second battery.
As has been described above, it is possible to permanently use a hand held device by using such a power supply method.